According to a conventional technique, by forming between a communications apparatus that transmits data and a communications apparatus that receives the data, plural transmission paths that sequentially relay the data via plural relay apparatuses, the arrival rate of the data is improved (for example, refer to Japanese Laid-Open Patent Publication No. 2010-11103). Further, according to another technique, the placement of communications apparatuses is adjusted such that plural routes are established between all communications apparatuses having a function of mutually relaying communications (for example, refer to Japanese Laid-Open Patent Publication No. 2010-45701). According to yet another technique, in a wireless multi-hop network, by presenting the distance to a node based on the hop count to the node, the installation position of the node is narrowed down (for example, refer to Japanese Laid-Open Patent Publication No. 2007-306280).
Among sensor network technologies, an arrangement has been proposed that is related to the placement of plural sensor nodes and that has high fault-tolerance (for example, refer to Mika ISHIZUKA, et al, “Stochastic Node Placement Improving Fault Tolerance in Wireless Sensor Networks”, Institute of Electronics, Information and Communication, Journal B, Japan, Nov. 1, 2005, Vol. J88-B, No. 11, pp. 2181-2191). According to another technology, the failure of a sensor node is detected by the transmission and reception of messages between sensor nodes (for example, refer to Yuichi KIRI, et al, “Differences between Centralized Control and Self-Organized Control in Robustness of Sensor Networks”, Institute of Electronics, Information and Communication, Technological Research Report, Network System, Japan, Jul. 12, 2007, Vol. 107, No. 146, pp. 1-6).
Plural transmission paths may pass through the same relay apparatus. If the relaying operation of a relay apparatus common to plural transmission paths is suspended consequent to a fault, battery exhaustion, etc., the transmission paths passing through this common relay apparatus become disconnected. If a relay apparatus is common to all of transmission paths and if this common relay apparatus suspends relaying operation, all of the transmission paths become disconnected and data cannot be transmitted. In other words, the wireless multi-hop network enters a non-functional state.
To prevent the wireless multi-hop network from entering a non-functional state, it is important to prevent a risky state in which all transmission paths transmit data through the same relay apparatus. Nonetheless, with conventional wireless multi-hop network technology, such a risky state in which all transmission paths transmit data through the same relay apparatus cannot be detected during operation of the network.